Seeing is Not Believing: People Do Not Overvalue Brain Images

May 28, 2013

Stock image; NIMH

Seeing a beautifully lit up image of the human brain is powerful – maybe too powerful, worry many scientists. But if you think that brain images are the most persuasive form of scientific evidence out there, think again, says a new study that examines how the public views neuroimaging. Members of the public are more savvy about brain images than the media and many scientists have come to believe.

“A lot of psychologists and neuroscientists have a love-hate relationship with functional neuroimaging,” says Martha Farah of The University of Pennsylvania. “Scientifically it’s an incredibly useful technology, and visually it’s gorgeous. But some have worried that imaging is too persuasive.”

Indeed, a well-known study published in 2008 in Cognition suggested that presenting brain images to readers was more convincing than presenting the same scientific evidence in other forms. “That finding fit with worries that had been brewing for a while, and so everyone cited that finding and assumed that the issue was settled: Brain images are very persuasive, perhaps too persuasive,” Farah says.

So Farah and research assistant Cayce Hook set out to replicate that study’s findings and then explore finer detail questions about how people interpret information from brain images. To their surprise, they were not able to replicate the findings – they found instead that the public does not over-evaluate brain images relative to others forms of scientific evidence.

In three experiments involving 988 participants, Farah and Hook asked laypersons to rate both fictional research descriptions and real science-news articles accompanied by brain scans, bar charts, or photographs. For example, in one experiment, participants viewed a description of a fictional study accompanied by either: a bar chart showing reduced activation of a brain area associated with self-control when obese subjects viewed food; an fMRI scan showing the brain areas lit up for non-obese versus obese subjects; or a photo of cookies.

While the fMRI images added interest level to the research descriptions, they did not affect how the participants evaluated the scientific reasoning behind the research. In the two other experiments, the researchers likewise found “little evidence of neuroimagingʼs seductive allure,” they write in the Journal of Cognitive Neuroscience.

“We were surprised to find that brain images had negligible effects on people’s judgments of research: Articles were rated the same, regardless of the type of image accompanying them,” Hook says. “We were encouraged when we discovered that several other research groups had also failed to replicate the original findings” of the 2008 paper.

The study also sought to test the idea that brain images appeal to people’s “dualism” – the idea that the mind is separate from the body. The opposing view “physicalism” follows the scientific idea that the that the mind cannot be separated from the brain, and that mental phenomena are states of the brain.

While they found that dualists did not react differently than physicalists to brain images versus other scientific evidence, they did find that they differed in their ratings of the articles themselves, which were all on cognitive neuroscience topics. “Overall, dualists found the research to be less convincing and less worthy of funding,” Hook says.

“Many neuroscientists worried that people would assume that brain images are like photographs of brain activity, and might consequently accept claims that are not well substantiated but accompanied by brain scans,” Hook says. But, the new research shows that “perhaps neuroscientists should give a bit more credit to the average person on the street: They don’t seem to be as easily dazzled by brain images as some have argued,” she says.

These worries have especially come to light recently on the issue of neuroscientific evidence in the courtroom. Many scientists have become concerned that brain images carry too much sway in court proceedings. On balance, however, “studies have found that although jurors may find neuroscientific testimony to be more convincing than other types of testimony, brain images on their own have little additional impact,” Hook says. “Our findings are consistent with this conclusion: it does seem that neuroscience may have special persuasive power, but this is not necessarily a property of brain images themselves.”

Indeed, Farah says: “There is plenty of reason to worry about the science literacy of the general public, but on this one question – whether people are swayed by seeing evidence presented as a brain image, compared to other kinds of representation – we are reassured!”